This invention relates to lubricating compositions used in admixture with fuels. More particularly, the present invention relates to lubricating compositions used in admixture with fuels which lubricants are employed to lubricate moving parts of 2-stroke engines.
In recent years, the evolution and technical progress in all types of internal combustion engines, and particularly in the field of 2-stroke engines, have led to engines of higher and higher horsepower. For example, outboard engines with a horsepower higher than 50 hp and even up to 100 hp and higher are commonly manufactured today. Another aspect of this evolution is the development of small air-cooled engines, not only for such vehicles as motorcycles, but also for chain saws, skidoos or snowmobiles, and the like. A feature of these engines is their high speed of rotation which results in their running hotter than their lower speed predecessors. Such evolution and technical progress has led to an increase in the severity of lubrication requirements for 2-stroke engines.
The lubricant useful in these new engines must form a stable and oily film, which at low temperatures will make easier the starting of the engine even under cold weather conditions. Additionally, such lubricant must perform well at the higher operating temperatures of the newer engines in order to avoid piston fouling, ring groove plugging and lacquering, formation of deposits, etc. which lead to a drastic reduction of power output and often results in expensive damage. Further, the exhaust gases resulting from the combustion of the fuel together with a part of the lubricant must be clean and have a minimum of the odors which are characteristic of most all 2-stroke engines. Other requirements, more particularly in the economic field, such as reduction of the oil to fuel ratio and a decrease in the amount of conventional additives, are coupled with the above criteria.
Several lubricating compositions for 2-stroke engines have been suggested to fulfill one or the other of the above criteria conditions. A feature of some of these compositions is the use of olefin polymers, more particularly polyisobutylene (which is readily available and inexpensive), as an additive for mineral or synthetic oil or base oil. In such compositions, polyisobutylene generally is added to the base oil in an amount which does not exceed 20% by volume. Usually, the polymers used in these known compositions are those having a mean molecular weight of between 10,000 and 15,000. It also has been suggested to add to the base oil, polyisobutylene in the form of an additive mixture comprising a major part of calcium petroleum sulfonate and a minor part of polyisobutylene, this additive mixture being used in an amount corresponding to about 1 to 5 volume % based on the total composition. These compositions have resulted in technical improvement when compared with prior and more conventional lubricants. However, these polymer containing compositions still have some disadvantages, particularly with respect to the thermal properties and cleanliness of the exhaust gases.
In order to overcome these disadvantages, lubricating compositions comprising a major part of polyisobutylene have been investigated. In such compositions, this polymer is mixed with a lubricating oil in an amount at least equal to the amount of this oil. Such compositions have shown favorable results and additional investigation has been carried out to further improve the qualities and performance of the lubricating compositions, particularly with respect to their behavior under high mechanical and thermal stresses for extended periods of time.
It is an object of the present invention to provide new and improved lubricating compositions.
Another object of the present invention is to provide new and improved lubricating compositions for admixture with fuels for 2-stroke engines.
A further object of the present invention is to provide new and improved lubricating compositions for admixture with fuels for 2-stroke engines which lubricating compositions have improved properties with respect to use under high mechanical and thermal stresses.
Additional objects will become apparent from the following description of the invention herein disclosed.